#include "math.h"
main()
{
    // lekai
    double e = 0.1, b = 0.5, c, d;
    long int i;
    for (i = 6;; i *= 2)
    {
        d = 1.0 - sqrt(1.0 - b * b);
        b = 0.5 * sqrt(b * b + d * d);
        if (2 * i * b - i * e < 1e-15)
            break;
        e = b;
    }
    printf("pai=%.15lf\n", 2 * i * b);
    printf("The number of edges of required polygon:%ld\n", i);
}